Svante Pääbo, a Swedish geneticist, received the 2022 Nobel Prize in Physiology or Medicine for his work. His research reshaped our understanding of human evolution. He founded paleogenomics, the study of extinct organisms’ genomes. Pääbo’s contributions explore our ancient past and genetic links to archaic relatives.
The Challenge of Ancient DNA
Working with ancient DNA presents challenges. Over thousands of years, DNA molecules naturally degrade into short, damaged fragments. Chemical reactions like hydrolysis and oxidation disrupt DNA structure, causing this breakdown. Older samples become more fragmented and altered, making genetic recovery difficult.
Contamination is another challenge. Ancient samples are easily infiltrated by DNA from microbes or modern humans during handling. This extraneous DNA can vastly outnumber authentic ancient DNA, overwhelming the target material. Researchers like Pääbo developed specialized techniques and strict protocols to isolate and authenticate degraded, contaminated ancient DNA.
Sequencing the Neanderthal Genome
Pääbo’s team successfully sequenced the entire Neanderthal genome. They used DNA from 38,000 to 44,000-year-old Neanderthal bones from Vindija Cave, Croatia. They developed methods to distinguish genuine Neanderthal DNA from microbial and modern human contamination. Advanced sequencing machines read the short, fragmented DNA strands.
The initial draft of the Neanderthal genome was published in 2010, revealing that modern humans of European and Asian descent carry Neanderthal DNA. This evidenced interbreeding between early modern humans and Neanderthals after migrating out of Africa, likely in the Middle East, 50,000 to 100,000 years ago. About 1 to 4 percent of DNA in non-African populations originates from Neanderthals. This gene flow suggests Neanderthal assimilation into the modern human gene pool, not complete replacement.
The Discovery of the Denisovans
Pääbo’s team also discovered the Denisovans, a previously unknown group of archaic humans. This began with analyzing a tiny finger bone fragment excavated in 2008 from Denisova Cave in Siberia. Mitochondrial DNA analysis showed this bone belonged to a hominin group distinct from modern humans and Neanderthals.
Nuclear DNA sequencing confirmed Denisovans were a sister group to Neanderthals, diverging 380,000 to 470,000 years ago. Denisova Cave has yielded only a few small, fragmented Denisovan fossils, including tooth and bone fragments. Similar to Neanderthals, Denisovans also interbred with human ancestors. Their genetic legacy is most pronounced in Oceanian populations, such as Melanesians and Aboriginal Australians, who carry 4 to 6 percent Denisovan DNA, with smaller proportions in East Asian populations.
Modern Human Genetic Legacy
Archaic DNA from Neanderthals and Denisovans influences modern human biology. These ancient gene variants shaped various traits and adaptations. For example, the Denisovan gene variant EPAS1 is prevalent in Tibetan populations, aiding high-altitude adaptation. This gene likely entered the modern human gene pool through interbreeding with already adapted Denisovans.
Neanderthal DNA also impacts our immune systems. When early modern humans migrated out of Africa, they encountered new pathogens. Interbreeding with Neanderthals provided advantageous gene variants for immunity, aiding adaptation to new disease environments. However, some Neanderthal-derived genes are associated with increased susceptibility to autoimmune diseases like Graves’ disease and rheumatoid arthritis, and influenced severe COVID-19 outcomes. Other Neanderthal genes link to traits like skin and hair, pain sensitivity, and fertility.